Wave transmission and modulation



Oct. 22, 1935. R A 5 G 2,018,401

WAVE T RANSMISSIQN .AND MODULATION Filed Oct. 25., 1920 v 2 Sheets-Sheet l //2 venfor Raymond A. fife/5mg.

. Oct. 22, 1935. v HE|$]NG I 2,018,401

WAVE TRANSMISSION AND MODULATION Filed Oct. 25, 1920 v 2 Sheets-Sheet 2 v /n venfor Raymond A. He/siny,

by @c/W A77).

Patented ct. 22,,

WAVE TRANSMESSEQN MWDULA'EKQN litaymond fr. Hcising, East @range, N. 5., designer to Western Eliectric Company, Incorporated, New York, N. Y a corporation of New York Application Gctober 25, 1920, Serial No. 419,221

4% Claims.

This invention relates to wave transmission and modulation systems and methods of modula tion. The principles "of the invention are illus-= trated by apparatus for the radio transmission of speech. The features of the invention are, however, equally applicable for the transmission of speech over wire lines and, for the most part, for use in wireless telegraph and wave transmission systems. y

In certain types of systems wherein a high frequency generator or modulator is associated with a space discharge variable impedance or amplifying tube, it has been found that disturbances often arise which transiently interfere with efllcient operation. While the cause of these disturbances is not wholly understood, it is .believed from experimental investigation that they are due to secondary electron emission in the Such secspech wave, signal wave or other wave causing the grid of the variable impedance tube to become highly positive, whereupon as soon as the secondary emission begins, a sudden change of grid potential occurs. This causes an impulsive disturbance or potential difference wave with a steep wave front to be impressed on the oscillator or modulator tube. Such waves may be analyzed intoa number of components, some of 'which are higher than essential speech frequencies. Whether or not this is the correct theory of the cause of the disturbing effects, it has been found that certain arrangements are effective in reducing'the number and violence of the disturbances which have been observed to occur.

Several means for accomplishing the desired result are illustrated. According to one method it is accomplished by including a choke coil between the oscillator and the variable impedance device. This coil is designed to have as low an impedance as possible for alternating currents having the frequencies corresponding to the essential frequencies necessary for the reproduction of speech and a relatively high impedance for waves of about five thousand cycles per second and upward. Impulsive waves, in being transdenly impressed upon the grid of the tube but not of such a large capacity as to shunt too much of the currents of speech frequency therethrough.

A third method is to place between an oscillator and ,thevariable impedance discharge tube a sectional filter of the low pass type whose cutofi limit is just above the highest of the essential frequencies of speech waves. In the case of signaling waves other than speech, the cut-off limit may be suitably modified in accordance cumstances.

When a filter of this type is used it has been found to have another important advantage.- All the harmonics and frequency components of speech which are above the essential frequencies are eliminated, with the result that the carrier wave is not modulated by them. In the ordinary case of a microphone feeding into a space discharge tube which in turn acts as a variable imwith cirpedance device to cause modulation, it has been found that a certain amount of distortion occurs in the microphone or the tube or both. Thus, if the band of speech frequencies represented by s is impressed upon the microphone, then components having the frequencies 2s, 3s, ete.,'willbe produced. Upon modulating with this distorted wave a carrier wave whose frequency is p, there will result in addition to the desired side frequencies pis, the frequencies 1112s, pi3s, etc. The transmitted band of frequencies is, for this reason, wider than necessary and these frequencies which result from the harmonics of the speech frequencies cause interference with other stations transmitting on closely adjacent wave lengths. By using a filter of the described type the modulating wave is limited to frequencies not greater than s and in consequence the transmitted band is limited to frequencies within the range 13:8 where 3- represents all the essential plishing this purpose are shown. The same filter which prevents shock excitation disturbances will also serve to eliminate the harmonics of the .4

speech waves and toreduce the undesired amplitude variations in the rectified current. However, other desirable forms of devices for eliminating the undesired amplitude variations may be utilized, and a variety of these are illustrated.

In the case where tuned circuits are used for this purpose any variation in the fundamental frequency of the alternating source of power will cause the harmonic frequencies to vary so that the tuned circuits, if adjusted correctly for one frequency, will not serve efliciently for other frequencies. For this reason, means are provided for automatically regulating the frequency of the source, particularly where this source is an inverted rotary converter.

Other objects and advantages of the invention will be apparent to those skilled in the art from a perusal of the following detailed description and the appended claims. The various novel features claimed and described are capable of use not only in the systems illustrated but in systems having similar characteristics.

In the accompanying drawings, Figs. 1, 2 and 3 represent various circuits wherein are included means for reducing the effect of shock excitation; Fig. 4 illustrates a circuit utilizing a direct current supply which is stepped up to the required voltage by means of a rotary converter and a transformation system, the current then being rectified by means of a vacuum tube system which also serves as a variable impedance system, and including means for eliminating the ripples from the rectified current; Fig. 5 represents a system similar to Fig. 4 wherein is used a three phase rotary converter and a slightly different form of ripple eliminating means.

In Fig. 1 the space discharge tube I is connected to a tuned antenna circuit 2 in such a manner that high frequency oscillations are generated in the antenna circuit. The frequency of these oscillations will depend upon the constants of the antenna circuit, namely the radiating capacity, the inductance 3 and the tuning capacity 4. A variable impedance tube 5 has its input circuit 6 connected to any suitable source 'I of speech or equivalent signaling waves, suchas a microphone circuit. The anode-cathode circuits of the tubes I and 5 are in parallel with respect to a source 8 of current and a speech frequency choke coil '8. A high frequency choke coil I0, which readily transmits currents of essential speech frequencies serves to prevent the high frequency oscillations generated by the tube I in theantenna circuit from being short-circuited through the tube 5 or the distributed capacity of coil 9. The elements so far described constitute a common type of radio telephone transmitter usually known as a constant current modulation system. It has been found that certain disturbances which appear to originate in the tube 5 transiently interfere with efficient working of the apparatus. These disturbances are believed to result from secondary electron emission in the tube 5 whereby sudden changes in potential of the grid of tube 5 tend to cause sudden changes in plate current. This results in impulsive disturbances being transmitted to and impressed upon the tube I. In order to smooth out these disturbances and reduce their amplitude, an inductance coil II is included in, series with coil I0. The coil II has characteristics intermediate between those of coils 8 and I0 and is designed to allow alternating currents having frequencies corresponding to the essential frequencies of speech waves to pass through readily but to attenuate waves of higher frequencies. Since impulsive disturbances are equivalent to high frequencies they will be smoothed out and attenuated.

In Fig. 2 the coil II is'omitted. In order to serve the same purpose, there is included a condenser I2 shunted across the input circuit 5 of the tube 5. This condenser serves to prevent sudden changes of potential of the grid of the tube 5. Its capacity is made sufficiently small so 5 that it will not act as a short circuit to speech currents. The production of impulsive disturbances by the tube 5 is prevented.

In Fig. 3 another means for serving the same purpose is illustrated. This consists of a filter F comprising a number of sections, each of which includes a shunt capacity I3 and a series inductance I4. This filter is preferably so designed as to have its cut-off limit at about the upper, limit of the essential frequencies in speech which is in. the neighborhoodof 3,000 cycles. The'manner of designing filters of this kind is described in published patents and need not be further described. The particular type of filter illustrated in Fig. 3 need not be used as others of different form may 20 .be designed which will accomplish the same purpose.

Fig. 4 illustrates a system for utilizing a source of direct current of relatively low voltage, for example 110 volts. The direct current supply circuit I5 is connected to a quarter phase inverted rotary converter I6. From this converter are taken off two alternating currents apart. Each of these phases may be stepped up to a desired high voltage, as for example 1,000 or 2,000 30 volts, by suitable transformers II. The high voltage secondaries of the transformers II are connected to a system of rectifying tubes I8 whereby the alternating current is rectified in order that it may be impressed upon and serve 85 as a power supply for the high frequency generating tubes I. The secondaries 20 each have a mid-point tap connection 2|. These midpoints are conductively connected by the conductor 22 to the cathodes 23 of the tubes I, while 40- tubes I8 have their anodes connected to the terminals of the secondaries 20 by the conductors 24. Assuming that the switch 25 is closed on the contacts 26 the path of the rectified current will be as fo1lows:beginning at secondary 20 45. through conductor 24, tubes I8, conductor 21. resistance 28, coil 29, switch 25, lead connecting contacts 26, coll III, tubes I and conductors 22, 2|, to the starting point. Connected across all of the filament-grid circuits of tubes I8 in par- I50 .allel is the secondary of transformer 3I, whose primary is included in a speech frequency or microphone circuit 1. The input circuit of the tubes I8 beginning at the grids, passes through the conductor 33, the resistance 34 and the sec- 55. ondary of transformer 3| in parallel, and the parallel combination of elements 28, 28, and 35 to the cathodes. Resistance 34 is the usual .means for lowering the impedance across the "Inductance coil 28 is included for a purpose here- 70- inafter described.

As the impedance of tubes I8 is made to vary in accordance with speech, the rectified current through the tubes I will be correspondingly varied, thereby causing the generation, in the an- 75 aorasoi tenna circuit 2,- of high frequency carrier current modified or modulated'in amplitude in accordance with speech. Since the rectified current resulting from the combination of the several phases of alternating current will have ampli= tude-variations corresponding to harmonics or multiples of the fundamental frequency, the current in the antenna 2 will also be modulated in accordance with these harmonic frequencies unless they are eliminated. One manner of elimi nating these frequencies is to shunt them out through several tuned circuits 3% shunted across the line from the switch to the conductor 22. Each of the several circuits at is tuned to resonance at one of the harmonic frequencies and as many of them are provided as there are troublesome harmonics. In the case illustrated where four phases are combined, the first harmonic will be four times the frequency of the fundamental.

enemy will appear in the rectified current. If,

however, there is unbalance either in the several phases, the transformers II, or the tubes l8, a component of fundamental frequency will be present. This component may be reduced in amplitude' and substantially eliminated by proportioning the condenser 35 and the coil 29 so that the circuits 28, 29 and 35 will be resonant at the fundamental frequency. If desired, one of the circuits 3B or 31 may likewise be tuned to resonance at the fundamental frequency.

Variations in the load upon the converter l6 tend to cause variations in speed thereof. The resulting changes in the fundamental frequency will be detrimental to emcient operation, since if the circuits 36 or 31 are appropriately attuned for one fundamental frequency they will not serve so emciently to eliminate the harmonics when the frequency changes. late the frequency of the converter I6, capacities 38a are connected across the several halves of the secondary windings 20 in shunt to inductances 39 which may be included in circuit by closing switches 40. Circuits 38a, 39 when tuned to the fundamental frequency which the converter It should produce will offer a non-reactive impedance as long as the frequency remains at the desired point. When the converter i6 speeds up the reactance of the circuits 38a, 39 will be capacitative and draw a leading current from the converter. On the other hand, when the machine slows down, the reactance of the circuits 38a, 39 will become inductive and produce a lagging component of current through the converter. Since a leading component of current through the rotary converter strengthens ,the field and tends to slow the machine up and a lagging component of current weakens the hold and tends to speed up the machine, a desirable regulating action will result. If the switches 60 are open and switches 4! are closed, so as to include in circuit the inductances 42, a similar regulating action will result provided the capacities 38 and the lnductances 42 are so propor- In order to regutioned with relation to the transformation ratio to the transformers l'l that they form a combination resonant to the fundamental frequency. The capacities 38a also serve to allow speech frequency variations to be shunted around the sec- 5 ondaries 2o. Owing to the high impedance of the secondaries 20 to speech frequency varia tions itis essential that the capacities 38a be provided. If neither of the sets of inductances 85 or 42 are included the capacities 38a will 19 take a very large leading current and thereby necessitate the use of a machine It having a larger current capacity as well as reducing the emciency.

In practice it is desirable that the fundamental 15 and principal harmonics of the alternating current should lie without the range of the essential frequencies of speech. This may be accomplished by causing the converterv it to generate a relatively low frequency, as for example 25 cycles, in which case the fundamental and the principal harmonics will be below the range of speech frequencies or by the producing from the converter it a relatively high frequency, as for example 2,000 cycles or upward, in which case the 5 fundamental and principal harmonics will be above the range of speech frequencies or in the upper and lessimportant part'of the range. In a well balanced four-phase system the fundamen; tal component will be small and a frequency of 500 or 600 may be used. The lowest harmonic will then be 2,000 or 2,400. The use of a rotary converter as a means of producing alternating current from a low voltage source of direct current is not necessary in case a suitable source of alternating current is available, since, in genera], the alternating current can be supplied in as many phases as desired and transformed to a suitable voltage. I

The grids of the tubes l are connected to the antenna system through a stopping condenser M. A leak path 43 extends from the grids to the cathodes 23. The leak path includes a resistonce 44 having a comparatively high ohmic value shunted by a capacity 45 and in series with the 45 inductance 6. The value of resistance 44 is a principal factor in determining the magnitude of the average negative charge upon the grids. However, as the cathodes and gridsare at varying and different relative potentials, a certain amount of high frequency energy tends to become dissipated in resistance 44. The source of high frequency voltage in the input circuit or grid-filament circuit is the condenser 4 through which the high frequency oscillating current set up in the antenna flows. Since coil 46 is not only required to act as a choke coil for high frequency current but should be designed sons to dissipate as little high frequency energy as possible, it consists of a winding having small diameter and length and consisting of a considerable number of turns in several layers of well insulated fine copper wire wound upon a wooden or other nonmagnetic and non-conductive core. Hysteresis and eddy current losses are thereby reduced to a minimum.

The distributed capacity of coil 46 should be as small as possible since the effect of such capacity in the coil is to act as a capacity shunt around the coil. The necessary value of induc- 7 tance of the coil 46 will depend upon the nature of the tubes, their electrical constants, the constants of the associated elements and the frequency of the oscillations produced.

- Referring again to the circuits 36, it will be notis transformed by a suitable three phase transformer system H, across the respective secondary windings of which, are connected the variable impedance rectifying tubes [8. The harmonic frequency components present in the rectified current will in this case comprise a triple frequency of the fundamental and other higher frequencies. In case the fundamental frequency is about 1,000 cycles or higher these harmonics may be eliminated by the filter F which is similar to the filter F of Fig. 3. A gang switch 25 is arranged to include in circuit either the filter F or the series of circuits 36. The circuits 36 are similar to the correspondingly numbered circuits in Fig. 4 and function in a similar manner, each being tuned to resonance at one harmonic frequency which it is desired to eliminate. The circuits 36, circuits 31, and filter F are equivalent arrangements, any of which may be applied to either Figs. 4 or 5. Anti-resonant circuits 38, 39 or 38, 42 are equally applicable to three-phase systems, such as disclosed in Fig. 5, and fourphase systems, such as disclosed in Fig. 4.

Having described in detail several forms of circuit illustrating the various features of the invention, the novel elements, combinations, and methods which are believed to be inherent therein are set forth in the appended claims.

What is claimed is: I

1. In a signaling system, a device having an output circuit for supplying high frequency wave. a variable impedance device for acting on saidfirst mentioned device in accordance with signaling waves, signaling wave transfer means connecting said devices and means connectedto said transfer means whereby signaling waves are transferred efiiciently between said devices and non-signaling waves originating in said variable impedance device are attenuated.

2. In a signaling system, a device having an output circuit for supplying high frequency waves, a variable impedance device for acting on said first mentioned device in accordance with signaling waves, wave transfer means connecting said devices, and means connected to said transfer means whereby signaling waves are transferred between said devices by impulsive disturbances originating in said variable impedance device having steep wave fronts are attenuated.

3. In a transmission system, a device having an output circuit for supplying high frequency waves, a variable impedance device for acting on said first mentioned device in accordance with signaling waves, wave transfer means connecting said devices, and a net-work comprising series and shunt elements connecting said devices whereby essential signaling frequencies are transferred between said devices and higher frequencies are attenuated or eliminated.

4. In a signaling system, a space discharge device having an output circuit for supplying high frequency waves, a space discharge device for acting on said first mentioned device in accordance with signals, wave'transfer means connecting said devices, and means connected to said transfer means whereby signaling waves are transferred efiiciently between said devices and non-signaling waves are attenuated. ll

tions, said devices having their output circuits 10 connected to said source, and impedance means associated with conductors connecting said devices whereby impulsive disturbances originating in said variable impedance device are highly attenuated or smoothed out before entering said 15 oscillation supplying device.

6. A modulation system. comprising a space discharge device having an output circuit for supplying high frequency oscillations, a second space discharge device connected to said first men- 20 tioned device, a control electrode in said second mentioned device, a source of waves for changing the potential of said control electrode in accordance with signals, conductive connecting means between said devices whereby said first men- 25 tioned device changes its operative condition in accordance with changes in the potential of said electrode, and means associated with said device whereby normal changes of potential of said electrode are prevented from affecting said first men- 30 tioned device.

7. In a modulating system, a high frequency electric discharge device, a low frequency electric discharge device, a common source of current supply for said devices, a plurality of con- 85 ductors'bonductive to direct current connecting different pairs of electrodes of said devices, and filter means comprising inductive reactance in series with said conductors and capacity reactances connected across said conductors. 4 8. The method which comprises simultaneously producing a unidirectional current from a multiphase alternating voltage, varying the'amplitude of the rectified current in accordance with signals, and selectively eliminating non-signaling amplitude variations.

9. The method which comprises rectifying a plurality of alternating currents not in phase, combining the rectified current, varying the amplitude of the combined current in accordance with signals, selectively reducing non-signaling amplitude variations in the rectified current, and controlling the generation of carrier oscillations thereby.

10. The method of producing a unidirectional voltage which varies in accordance with signals which comprises variably impeding and combining the half waves of a plurality of phases of alternating current and selectively'reducing nonsignaling variations in the resulting current. v o

11. The methodof producing a unidirectional current which varies in accordance with signals which comprises variably impeding and combining the half waves of a plurality of phases of alternating current and selectively reducing those amplitude variations in the resulting unidirec- I .tional current which have a frequency equal to in the resulting rectified current due to the combined half waves of said phases. 2

13. In a'jtransmission system,:a device for the productio of carrier waves which vary in accordance with signals, a plural-phase source of a1- ternating current for supplying saiddevice, rectifiers for the several phases of said source in circuit with said source and said device, signaling means for varying in accordance with signals the impedance of said rectifiers, and selective. circuit means for eliminating the ripples in the rectified current due to the combined half waves of said phases.

14. In a transmission system, a device for the production of carrier waves, a plural-phase source of alternating current for supplying said device,

rectifiers for the phases of said source in circuit;

with said source and said device, signaling means for varying the impedance of said rectiilers, and

selective circuits for discriminating between the;

signaling variations and the amplitude variations dueto the combinedhalf waves of said phases in the resulting'rectified current. i

15. In a signaling system, an alternating current source of such a frequency and number of phases that none of the important harmonics thereof fall in the range of the essentialfrequencies of audible speech, a rectifying system for said current, means for varying the impedance of said rectifying system in accordance with speech waves, means for supplying the resulting rectifying current to a modulated wave producing device, and means for selectively eliminating at least one important harmonic component of the rectified current.

16. In combination, a plural phase source of alternating current, a rectifier for each phase thereof, a common line for carrying rectified current, a load device connected into said line, and means forcausing the rectified current supply to said load device to vary in accordance with signals, said line comprising circuits of high im-.

pedance to current variations due to the combin .ing of said phases but of low impedance to current variations corresponding to said signals.-

17. In a signaling system, an electron discharge device, a plural phase source of alternating current, a rectifying device for each of the phases, a plurality of circuits, each of said circuits being supplied with current of one phase from said plural phase source and including one of said rectifying devices and said first named electron discharge device, means for synchronously varying the impedance of said rectifying devices in accordance with signals, and devices in shunt to said first named electron discharge device, said last named devices being of low impedance to current variations due to combining said phases of high impedance to current variations corresponding to said signals.

18. In combination, a plural phase source of alternating current, a rectifier for each phase thereof, a line for carrying the resulting combined rectified current, a modulating device connected to said line, means for varying the current in said line in accordance with speech, and a filter across said line having -an upper transmission limit approximately equal to the highest frequencies necessary for the reproduction -01 speech.

19. In a signaling system, an inverted rotary converter, means for controlling the frequency of said converter comprising impedance means in the load circuit thereof having capacitative reactance. at higher frequencies and inductive reactance at lower frequencies than the frequency 1 desired from said converter, rectifying means constituting a load circuit for said converter, 'a circuit tuned to a mulitple of said desired'frequency in circuit with said rectifying means, and 5 a signal controlled device supplied with the rectlfied current.

20. In a signaling system, an inverted rotary converter, means for controlling the frequency of i said converter comprising a loop-resonant circuit connected in the load circuit, said loop circuit. being tuned to resonance at the frequency desired to be produced by. said converter, and a load circuit for said converter including a signal controlled space discharge tube, and a circuit for suppressing a current component which 'has a frequency equal to a multiple of the frequency at which said loop circuit is resonant.

21. In combination, a plural phase source of alternating current comprising an inverted ro-' go tary converter, a rectifier for each'phase thereof. and a common line for carrying the rectifying current, tuned circuits associated with said linefor eliminating harmonic frequencies due to the combination of said phases, and regulating means for maintaining constant the speed of said con-r verter whereby said circuits will operate without readjust. I 22. In an electrical system, a discharge device,

an impedance varying element therefor, a leak path therefor, said leak path comprising a radio frequency choke coil having negligible distributed capacity, hysteresis and core losses.

24. A modulating system, comprising a plural phase source of alternating current, a space discharge device for rectifying and combining in a circuit the. current of said phases, means for supplying the combined current to a modulating device, a resistance means in said circuit, an impedance control element for said space dischargedevice, and a tap connection from said circuit to said element whereby a suitable working potential is applied to said element.

25. In a modulating system; a high frequency. space discharge device, a low frequency space discharge device, a source and a circuit in common to said devices all in series for supplying energizing current to the space current paths thereof; a resistance in said circuit; and a control element for one of said devices, said element being connected to said circuit by means whereby the drop of voltage across said resistance serves to establish the working potential of said element.

26. A transmission system comprising a low voltage source of, direct current, a rotary converter for transforming said current into alternating current, a transformer for the alternating current, means associated with said transformer for regulating the frequency of said converter, rectifiers for the transformed alternating current, and an oscillation generator controlled by the rectified current.

fied current for maintaining said oscil1ations,"

and means traversed by said rectified current for suppressing ripples therein. a I

28. In an electric energy translation system, a source of two-phase current, a space discharge rectifier connected to said source, a space discharge amplifier and an oscillator supplied with current from said rectifier, and means for eliminating harmonics from said current, said means comprising an anti-resonant circuit in series with said oscillator and a series resonant circuit in shunt thereto.

29. An audio amplifying apparatus having means for quieting the amplifying element, said apparatus including a source of energy, a plate arranged to attract ions from said source, a grid appropriately disposed between said source and said plate, and a high reactance-in circiut with said grid and said source, said means being additional to said source and said grid and arranged to receive the entire static charges of. electricity developed by said source.

30. An audion receiving system having an ordinary amplifier, the grid of said amplifier being included in a circuit upon which the received oscillations are impressed, and means for preventing undesired oscillations in said grid circuit, comprising a condenser having a capacity so proportioned to the capacity of the grid as to receive and retain the ionically produced charges which tend to accumulate on said grid.

31. A thermionic amplifier combined with means for preventing inherent oscillations in the grid circuit thereof, comprising a high reactance and a condenser shunted across the filamentgrid circuit.

32. A radio apparatus having a thermionic amplifier and containing means for preventing inherent oscillations in said amplifienincluding an audio-frequency step-up transformer and a condenser disposed between said amplifier and said transformer and shunted acrossthe filament-grid circuit of the apparatus for accumulating the entire static charge of negative electricity developed by said amplifier, the ions and the grid of said amplifier constituting a conductive path communicating with said condenser.

33. A. radio apparatus having a three-electrode thermionic amplifier and means for preventing inherent oscillations in the filamentgrid circuit thereof, including a step-up trans former and, between the secondary winding of said transformer and the amplifier, a currentqualifying shunt extending across the filamentgrid circuit.

34. A radio signaling system, comprising an antenna earth system, a plurality of vacuum tubes having hot and two or more cold electrodes, means for associating said cold electrodeswithsaid antenna earth system,andwith said hot electrodes,

and a vacuum tube interposed between one set of cold electrodes and the filament electrodes whereby the space between the electrodes of said last mentioned vacuum tube constitutes a resistance for varying said resistance by and in accordance with signals. 36. Apparatus for producting oscillations comprising; a source of polyphase alternating current, thermionic oscillation-producing means compris- 5 ing an anode, a cathode, a control electrode, and coupled circuits connecting said anode and control electrode with said cathode; and means for delivering potentials corresponding to waves of both signs from. the diiferent phases of said 10 polyphase source to said anode-cathode circuit. 3'1. In combination, an electronic emission device having an electron emitting electrode, and a plate electrode, means for imposing a potential upon the plate electrode thatis 'positive with 15 respect to the electron emitting electrode, said means having a variable potential, means operating in response to the size and direction of the current variations due to variations in said potential to affect the space between the electron g0 emitting electrode and the plate in such a sense as to tend to maintain the space current constant in spite of said variations, and means cooperating with said afiecting means for allowing impedance variations in the path to vary the current in said path. 7

38. In combination, an electronic emission device having an electron emitting electrode, and a plate electrode, a circuit connecting said electrodes, said circuit including a source of varias able potential for impressing a potentialupon the plate electrode that is positive with respect to the electron emitting electrode, means aflecting the impedance of this circuit in response to each variation of current due to variations in said po- 8 tential, in such a sense as to tend to maintain the space current constant in spite of the fluctuations, other means causing additional variation in impedance in the space between the electrodes, and means cooperating with said aflecting means 40 and operating in response to such variations in impedance for allowing the impedance variations to affect the current flow in said circuit.

39. In a system for supplying operating voltages to an-electron discharge device having a cathode, an anode and a grid, a source of periodically fluctuating voltage, a resistance connected to said source and individual connections from each of the electrodes of said device to said resistance, said connections being so made that the potential impressed from said resistance upon the grid is always negative with respect to that .of the cathode and fluctuates in opposite phase to the voltages fluctuations impressed upon the anode. ll

- 40. In'a system for supplying operating voltages to an electron discharge device having a cathode, an anode and a grid, a source of voltage having a fluctuating component of particular frequency, an impedance including resist- Q ance and reactance elements connected to said source and individual connections from each of the electrodes of said device to said impedance, said connections being so made: that the potential impressed from said impedance upon the grid is always negative with'respect to that of the cathode and fluctuates in opposite phase to the voltage fluctuations impressed upon the anode and said reactance being proportioned to reduce in amplitude and substantially eliminate I in the anode circuit of the device current fluctuations of said particular frequency.

41. In combination, an electron discharge device having a cathode, an anode and a grid, a source of periodically fluctuating anode 1199 16 42. In combination, a space discharge device comprising a cathode, an anode and a grid, a

power source for supplyingvoltage to the anode circuit having a power frequency component and means to suppress in the anode circuit currents of the frequency of said power component comprisin'g impedancemeans selectively developing between its terminals a difierence of potential at said power frequency large compared to that of desired other components, said impedance means being common to the grid-cathode and anode-cathode circuits of said device.

43. In combination, a space discharge tube having a cathode, an anode and a grid, a source of power voltage supply for said device, said source having a power frequency fluctuation tending to produce currents of the power frequency in the anode circuit of the device, and means to reduce and substantially eliminate production of such currents of the power frequency in the anode circuit comprising an im- 5 pedance combination efiectively coupled to the grid-cathode circuit of the device and effectively introducing into the anode-cathode circuit of the device a high impedance selectively at said power frequency.

10 44. In combination, a space discharge device having a cathode, an anode and a grid, a source of power current for energizing said device, having a power frequency component tending to produce undesirable fluctuations in the anode 15 current of the device, and a frequency-selective circuit for selectively impressing on the grid of the device a voltage of the power frequency to 'the exclusion of voltage of desired other fre-.

quencies in such manner as to reduce and sub- 20 stantially eliminate anode current fluctuations of said power frequency.

RAYMOND A. HEISING. 

